1. Field of the Invention (Technical Field)
The present invention relates to the in-situ removal of contamination from ground water and soil. More specifically, the invention is a process and apparatus that enhances the oxygen, temperature, and other subsurface conditions to promote the physical, biotic, and abiotic removal of organic and some inorganic contamination from ground water and soil.
2. Background Art
Soil and ground water may be contaminated as a result of a release of compounds due to spills; leakage from storage, leaching of waste materials or by intentional acts such as dumping. Biodegradation of organic compounds by aerobic process can occur in the first three (3) feet below the earth's surface where oxygen is available from exchange with ambient air. However, if not isolated or removed that portion of the contamination below three feet largely remains unaffected by natural processes and commonly spreads. Oxygen normally can not reach this depth and conditions needed for anaerobic decomposition of the contamination are commonly not present (e.g., sufficient heat, mass of organics, nutrients, etc.).
Many methods and apparatus exist for decontaminating soil and ground water from compounds such as hydrocarbons and other organic and inorganic compounds. Common to these inventions are complex and elaborate means for achieving such decontamination by introducing heat and oxygen to a targeted area.
U.S. Pat. No. 5,601,382 to Corte et al. teaches an in-situ thermal system for decontaminating soil utilizing a sunlight transmitting, non-porous cover that allows solar energy to enter. Removal of contamination occurs as a result of a greenhouse effect in which trapped solar energy heats the interior air within the covering and in-situ soil below, vaporizing contaminants in the soil near the surface. This system is limited to decontamination of soil near the surface through assisted heating.
U.S. Pat. No. 4,765,902 to Ely et al., teaches an in-situ biodegradation system for hydrocarbon contaminated soil. Removal of contamination from soil occurs by evacuation of gas at high rates from bore holes drilled into the contaminated soil using a pump as a vacuum source. Evacuation of gas from the bore holes draws oxygen into the contaminated zone from the ground surface. Hydrocarbons and soil moisture are removed by evaporation, biodegradation, or creation of a hydrocarbon aerosol. This system requires significant power usage to create the vacuum needed and is limited to decontamination of soil. Removal by biodegradation is limited by the low temperatures that naturally occur below the earth's surface, and by the availability of moisture under vacuum conditions.
U.S. Pat. Nos. 4,593,760, to Visser et al, and 4,183,407 and 3,980,138, both to Knopic teach a system where evaporation of hydrocarbons in underground soil may be achieved by forced venting. However, this process is limited by the vapor pressure of the spilled hydrocarbons and the amount that can be evaporated. Since there is a limit on the amount of hydrocarbon that can be evaporated by venting, there is no incentive to go above a flow rate that provides the maximum evaporation. This system requires power usage for forced venting and is limited to decontamination of soil. Removal by biodegradation is limited by the low temperatures that naturally occur below the earth's surface.
Biodegradation has also been disclosed for underground hydrocarbons. U.S. Pat. No. 4,401,569, to Jhaveri et al, discloses a method and apparatus for treating hydrocarbon contaminated ground and ground water. Patentees disclose adding nutrients and gases to water that is flowed through the contaminated soil. A process of this type can be disadvantageous because: the irrigation water washes some hydrocarbons or other contaminants (toxic metal salts, etc.) into the water table; water carries a limited amount of oxygen (8 ppm) into the soil which limits the amount and the rate of degradation that may take place, irrigation can limit biodegradation by physically channeling oxygen-carrying fluids away from the hydrocarbon contaminated (oily) dirt.
Accordingly, there is the need for a process that will remove contamination from both soil and ground water though enhancement of natural removal mechanisms in an efficient and environmentally acceptable manner. This need has now been satisfied by the invention that is described below. Although each of the foregoing patents disclose devices and processes which are satisfactory for their intended purposes, none discloses a method or apparatus for decontaminating soil and ground water in the manner that is claimed herein: